Rotary compressing,displacing or expanding machine

ABSTRACT

A rotary fluid compressing displacing or expanding machine of the type in which lobes on a rotor rotate within a casing relative to blades which are rotatably mounted on the casing so as in sequence to form a barrier to the passage of fluid and by their rotation permit passing of the lobes to cause a continuous delivery of fluid in front of the lobes and intake of fluid behind the lobes. With the object of achieving a lower than usual noise level and an increased fluid displacement for a given casing diameter, an improved machine is characterized in that the tips of the blades sequentially form a sealing clearance with an inner surface of the casing which is concentric with the rotary axis and further in that the blade thickness to width ratio is in the range of 0.4/N to 0.9/N where N is the number of blades.

United States Patent 11 1 [111 3,811,807 1451 May 21, 1974 TryhornROTARY COMPRESSING, DISPLACING OR' EXPANDING MACHINE [75] InventorsDonald Wilfred Tryhorn, Slough,

' England [73] Assignee: I Sir W. G. Armstrong Whitworth &

Company (Engineers) Limited, Slough, Buckinghamshire, England [22]Filed: June 15, 1972 [21] Appl. No.: 263,095

[30] Foreign-Application; Priority Data June 17, 1971 Great Britain28424/71 [52] US. Cl. 413/227 1 [51] Int. Cl. F016 l/00 [58] Field orSearch.... 418/227 [56] References Cited Y i 2 UNITED STATES PATENTS1,101,329 6/1914 Reaugh" 418/227 1,394,861 10/1921 I 2,341,7 0 2/1944l2/l959- Tryhorn 418/227 7/1957 Vamane 418/227 Primary Examiner-C. J.Husar Attorney, Agent, or Firm-Holmar1 & Stern [57] ABSTRACT A rotaryfluid compressing displacing or expanding machine of the type in whichlobes on a rotor rotate within a casing relative to blades which arerotatably mounted on the casing so as in sequence to form a barrier tothe passage of fluid and by their rotation permit passing of the lobesto cause a continuous delivery of fluid in front of the lobes and intakeof fluid behind the lobes. With the object of achieving a lower thanusual noise level and an increased fluid displacement for a given casingdiameter, an improved machine is characterized in that the tips of theblades sequentially form a sealing clearance with an inner surface ofthe casing which is concentric with the rotary axis and further inthat'the blade thickness to width ratio is in the range of 0.4/N to0.9/N where N is the number of blades.-

4 Claims, 2 Drawing Figures EXPANDING MACHINE BACKGROUND OF THEINVENTION The invention relates to rotary fluid compressing, displacingor expanding machines of the kind known as blade-type blowers and hasbeen devised with the object of improving said machines by reducingtheir noise level and increasing the fluid displacement for a givencasing diameter;

The specification of British Pat. No. 804,602 sets out the cycle ofoperation of this type of machine in which lobes mounted on a rotorrotate within a casing relative to blades which are rotatably mounted onthe casing so as in sequence to form abarrierto the passage of air andby their rotation permit passing of the lobes to cause a continuousdelivery of air in front of said lobes and intake of air behind saidlobes.

In this type of blower there are three major sources of noise, due to: t

1. the explosions of pockets of air carried over from the delivery spaceto theintake space.

2. Changes in velocity of the intake air due to variations in theeffective area causing displacement with changes in rotor position. 3;.The implosion of air from thedelivery space to air trapped between theintake and'delivery spaces. Each of these excites airpressurefluctuations" and thus, results in noise. The latter excites themechanical vibrationof the blade which resists the implosion. I

, Any part of the air circuit which forms a pipe amplifies noise when apressure disturbance excites its natural frequency, and harmonics.

The only type of blade type blower which does not give rise to conditionl) viz. pockets of air carried over from the delivery space tothe intakespace, has

thin-parallel sided blades..These offer a continuouslychanging'projectedarea to the rotatinglobes and since a varying rate offlow is created, therefore condition (2) exists. Furtherthe thin bladesofferlittleresistance to. b nd n -and. -qqnditiqafil isi'a some .9!

channel within which the bladesforma barrier. This revolvesinside astationary casing andthus, the fulldiameter of the machine isnot usefulworking space. To utilize the space'fully the blad'etips shouldsealdirectly on the outer case. Whenthis is done" with the known type ofblower, the recesseslin the-casing which maintain the seal over theblade spacingperiod-formaddi tional pockets of air to cause explosionnoise.

In known types of this blower, when contact is made between the trappedair space and the delivery'space the natural geometry of thestructure'causesa rapid increase in area of contact and thus, a largepressure wave enters the trapped volume exciting noise and bladevibration.

acterized in that the tips of the bladessequentially forma sealingclearance with aninner surface of the casing which is concentric withthe rotor axis and that the blade thickness to width ratio is in therange of 0.4/N to 0.9/N, where N is the number of blades.

The thickness of the blades is determined by the angle through whichthey turn over the period of the trapped volume and on the profile ofthe blade tip. The gap between the lobes has a width sufficient to passthe hub part of the blades and since the tips approach this gap at anangle, the thickness is not truly uniform but tapers with reducingthickness towards the outside diameter of the blade. The curvature ofthe blade may be approximate to the arc of the circle having a radius of2d /t, where D is the pitch circle diameter of the blades and t is thetip thickness thereof. 7 Some compensation can be made for the reductionin the sealing period resulting from the narrowing of the blade tips bynot having these concentric with the blade center but made to a largerradius. This reduces the leakage gap at the beginning and end of thesealing period. The machine may thus have the tips of the blades made toa radius larger than half the blade width.

A lowrate of pressure-increase in the trapped volume is achieved bykeeping it sealed from the intake space for a period and permitting acontrolled rate of leakage from the delivery space to raise thepressure.

It may be arranged that such controlled leakage causes the start ofcompression.

Any rapid change of pressure on one side of a blade causes bending andvibration of the blade and its shaft; thus, noise is created. With theknown cantilever blades this can be reduced by the use of blades whichare thick at'thesupporting end.

The susceptibility of the blade to bending and vibrating also dependsupon the method of mounting the blade. By use of a ring mounted onspacer pieces between the blades additional bearings can be mounted.This allows the .blades to be doubly supported instead of cantileversupported.

The invention thus may further provide for the blades to be supported atboth ends. 7

When portsare cut in a rotor for the passing of the air, the flow lossthrough them sets an economic limit to the speed'ofoperation. Also, thedistance from the port to the blade which forms the end of the workingspace associated with that port creates a pipe length in which airpressure waves create noise.

Both these conditions can vbe avoided by eliminating the end disc of therotor andhaving a rotor in the form of a bar having to one side of itsrotation axis radially inner and outer lobes and to the opposite side ofits rotation axis a plate which makes sealing clearance with the end ofthe blade which forms the barrier to the passage of fluid. Further, aduct which rotates with the rotor may separate the intake and deliveryair flows. By this means the area available for the passage of air atthe sides of the rotor is greater than the effective pressure applyingarea of the lobes and thus, there is no restriction to flow where theair passes the plane of the rotor.

BRIEF DESCRIPTION OF THE DRAWING A particular and at present preferredimproved' blower in accordance with the invention is hereinafterdescribed by way of example with reference to the drawing whichaccompanied the specification, wherein:

FIG. 1 is a transverse section of the blower and the working space sweptby the lobes, and

FIG. 2 is a longitudinal section on the line XYZ of FIG. 1, showing theair ducting and blade mounting.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The blower of FIGS. 1and 2 comprises a cylindrical casing l in which runs concentrically abar or anchor type rotor comprising an inner sealing hub 2 and a radialbar 3 which support a radially outer lobe 4, a radially inner lobe 5,and the radially inner and radially outer sealing plates 6 and 7 whichseal the ends of the blades 8 when they contain between them the trappedair volume of a working space 9. The thickness of these blades is suchthat there is always an effective seal on the bore of the casing betweena delivery space 10 and an intake space 11. In order to pass between thelobes 4 and with a constant clearance at the various angles of rotationthe thickness of the blades is reduced from the parallel towards theends. A curve having a radius of 2 X blade pitch circle diametersquared/bladethickness is satisfactory, but within normal limits ofcleamace an approximation of this shape may be made up of flat planes.

A continuous seal must be obtained between the delivery and intakespaces at the lobes, and where the lobes pass from one blade tip to thenext, concentric stationary spacing pieces 12 are used to fill the gapsbetween the blade tips.

The sealing plates 6 and 7 are preferably made to cover a larger arcthan the trapped air volume 9. This gives a period of time over whichcompression takes place. The rate of compression is controlled by theleakage around the blade on the delivery side and the rotor hub may becut away at 13 to give the requisite leakage flow rate. It is moreconvenient however to have groove holes formed in the sealing plates 6and 7 to yield this controlled increase in leakage compression.

In FIG. 2 there is shown a ring 14 mounted on the spacing pieces 12 andwhich supports the blades 8 at their ends remote from the backplate 15.Further, the ring 14 runs in close fitting grooves between the lobes 4and 5 and the two parts of the sealing plates 6 and 7. The air intakefrom the casing 16 to the working space 11 is via a rotating duct 17which maintains an air seal between the casing 16 and the casing 1. Theair is delivered from the working space to a delivery casing 18 roundthe outside of this rotating duct and thence to a delivery flange 19.

The design as described satisfies the object of the invention andprovides a machine having a minimum of sources of noise in that:

1. There are no pockets of air carried over from the delivery to theintake space:

2. The effective area causing displacement remains substantiallyconstant. Also, the projected area of the rotating lobes remainsconstant so that if the projected area of the blades were also constantthen the air flow into the machine would be steady. By choosing a bladehaving a tip thickness 1 and diameter d to give a t/d ratio within therange of 1.4/N to 0.9/N where N is the number of blades and by suitablechoice of the blade tip radius it is arranged that the projected area ofthe outer half of the blade does remain substantially constant. At

the center hub the effective area causing displacement is low and smallchanges in projected area of the blades are acceptable because theycause little change in rate of the total air intake.

3. The implosion of air from the delivery space to the trapped volume isbrought to a low level of intensity by making it take place over a longtime period. The rate of leakage is controlled by profiling one of therotating surfaces which makes a seal on the blade, as depicted by thecut away part 13. To avoid too rapid an increase in leakage area, theblade tips tend to seal again towards the end of the part 13 tocompensate for the rapid increase in leakage area at the outer bladetip. The leakage compression period can be made equal to one quater ofthe blade separation angle or cyclic repeat time which in the machine ofFIG. 1 is or four cycles per revolution and the compression period22.5". The pressure rise in the trapped volume although a little fasterthan that given by a piston in a cylinder is slower than the so-calledback flow compression of the Roots type blower. The trapping blade issubject to this rising pressure on one side and inlet pressure on theother. This causes bending of the blade and it is a feature of thedesign that the natural frequency of bending of the blade is highcompared with the frequency of blade loading by compression pressure. Itis to assist in achieving this feature that the blade is supported atboth ends by the ring 14 as previously explained instead of by acantilever arrangement.

vAir pressure disturbance can be reduced, but not eliminated. Eddynoises of air passing through the working clearances remain, even withsteady flow. It is possible however, to reduce the amplification givento such noises, and other pressure changes, by not letting them exciteair vibrations in pipes.

The working spaces within the machine become definable as pipes whenevera port causes a restriction and so define a length from this restrictionto the closed end which may be the sealing blade. For this machine arotor design is shown which does not have ports.

The inlet and delivery working spaces 11 and 10 are in full andcontinuous communication with the duct openings in the casings l6 and 19via the rotating duct 17 and the delivery casing 18. The anchor typerotor comprises a bar 3 supporting at one end the lobe 4 and at theother end the sealing plate 7 and being mounted on the driving shaft.This bar is narrow, so that it does not form an end wall to the workingspaces. The thickness of this bar may be increased locally as weight tocorrect the dynamic balance of the lobes and sealing plates, as shown at20 in FIGS. 1 and 2.

Each blade 8 is mounted on a shaft passing through the back plate 15 andprovided with a gear 21 which engages an intermediate gear 22 itselfengaging a gear 23 on the driving shaft of the machine. The ratios ofthe gears are so chosen that each blade makes one revolution for eachtwo revolutions of the driving shaft. Other forms of reduction gear maybe used to obtain this drive ratio.

The machine can be run as a compressor, as a displacing or meteringdevice or as a motor. The fluid flow may be reversed for a givenrotation by turning the rotating duct 17 by relative to the rotor.

I claim:

1. A fluid compressing, displacing or expanding machine comprising: astationary casing having a cylindrical bore with a perpendicular endface, said casing having inlet and delivery openings disposed on theexterior thereof;

i a plurality of blades mounted intermediate their ends within said borein said casing for rotation about fixed axes parallel to the axis ofsaid bore and spaced from one another circularly about the bore axis;

stationary pacing pieces disposed intermediate adjacent blades on thesame radius as the axis of rotation of said blades;

a rotor rotatably mounted in said casing and being co-axial with saidbore, said rotor having a pair of radially aligned lobes disposed on oneside of the rotor axis;

an outer one of said lobes being disposed closely adjacent the surfaceofsaid bore in said casing and an inner one of said lobes terminating in asealing hub disposed on the opposite side of the rotor axis from saidlobes; said lobes being spaced apart from one another to permitwidthwisepassage of each blade and each stationary spacing piece as said rotorro- .right angles to the radius of said bore on the side i of said rotorhaving lobes to provide a seal between the surface of said cylindricalbore and said sealing hub when in the former direction, and

,to allow said blades to pass between said lobes when in the latterdirection;

a plate mounted upon said rotor on the side of the axis thereof oppositeto said lobes and at right angles to said axis which makes sealingclearance with the ends of said blades when each blade is in its radialdirection relative to the axis of said bore in said casing; and

passageways being rotatable with said rotor for the intake and deliveryof fluid at opposite sides of said lobes and communicating with saidinlet and delivery openings on the exterior of said casing.

2. A machine as claimed in claim 1, wherein said blades are parallelsided with a thickness to width ratio in the range of 0.4/N to 0.9/Nwhere N is the number of blades and the inner surface of said casing iscylindrical throughout.

3. A machine as claimed in claim 1, in which the ends of said blades aremounted in bearings supported by a ring fixed in spaced relation withinsaid casing.

4. A machine asclaimed in claim 2, in which the tips of said blades aremade to a radius larger than half the blade width.

1. A fluid compressing, displacing or expanding machine comprising: astationary casing having a cylindrical bore with a perpendicular endface, said casing having inlet and delivery openings disposed on theexterior thereof; a plurality of blades mounted intermediate their endswithin said bore in said casing for rotation about fixed axes parallelto the axis of said bore and spaced from one another circularly aboutthe bore axis; stationary pacing pieces disposed intermediate adjacentblades on the same radius as the axis of rotation of said blades; arotor rotatably mounted in said casing and being co-axial with saidbore, said rotor having a pair of radially aligned lobes disposed on oneside of the rotor axis; an outer one of said lobes being disposedclosely adjacent the surface of said bore in said casing and an innerone of said lobes terminating in a sealing hub disposed on the oppositeside of the rotor axis from said lobes, said lobes being spaced apartfrom one another to permit widthwise passage of each blade and eachstationary spacing piece as said rotor rotates; drive means associatedwith said rotor and said blades for turning said blades about their axisat the speed of said rotor, as said rotor rotates, from a radialdirection in said bore to a direction a right angles to the radius ofsaid bore on the side of said rotor having lobes to provide a sealbetween the surface of said cylindrical bore and said sealing hub whenin the former direction, and to allow said blades to pass between saidlobes when in the latter direction; a plate mounted upon said rotor onthe side of the axis thereof opposite to said lobes and at right anglesto said axis which makes sealing clearance with the ends of said bladeswhen each blade is in its radial direction relative to the axis of saidbore in said casing; and passageways being rotatable with said rotor forthe intake and delivery of fluid at opposite sides of said lobes andcommunicating with said inlet and delivery openings on the exterior ofsaid casing.
 2. A machine as claimed in claim 1, wherein said blades areparallel sided with a thickness to width ratio in the range of 0.4/N to0.9/N where N is the number of blades and the inner surface of saidcasing is cylindrical throughout.
 3. A machine as claimed in claim 1, inwhich the ends of said blades are mounted in bearings supported by aring fixed in spaced relation within said casing.
 4. A machine asclaimed in claim 2, in which the tips of said blades are made to aradius larger than half the blade width.